This invention relates to a test head for a semicondcuctor integrated circuit (IC) tester.
U.S. patent application Ser. No. 11/024,536 filed Dec. 28, 2004 describes a semiconductor integrated circuit tester comprising a test head that includes a circular device interface board (DIB) having an annular array of contact elements exposed at the underside of the DIB, and an annular support frame that is located below the DIB and is moveable vertically relative to the DIB. The support frame defines multiple radial slots that accommodate respective electrical connectors, which may be as described in co-pending patent application Ser. No. 10/802,993 filed Mar. 16, 2004. Each connector includes a cable positioning block in which the ends of multiple coaxial cables are held, with the conductive cores of the coaxial cables constituting contact elements that are exposed at the upper surface of the positioning block and vertically aligned with respective contact elements of the DIB. Ideally, the upper surfaces of the contact elements of the connector would all lie in a common horizontal plane and the lower surfaces of the contact elements of the DIB would all lie in a common horizontal plane so that vertical movement of the support frame would result in the contact elements of the connector simultaneously contacting the corresponding contact elements of the DIB. However, in practice the upper surfaces of the contact elements of the connector do not lie in a common horizontal plane and the lower surfaces of the contact elements of the DIB do not lie in a common horizontal plane.
We can define the contact plane of a connector as the plane for which the sum of the squares of the distances of the upper surfaces of the contact elements of the connector from that plane is a minimum and similarly we can define the contact plane of the corresponding group of contact elements of the DIB as the plane for which the sum of the squares of the distances of the lower surfaces of the contact elements from that plane is a minimum. It is possible to manufacture the connector so that the variance in distance of the upper surfaces of the contact elements from the contact plane of the connector lies within a narrow range. Similarly, it is possible to manufacture the DIB so that the variance in distance of the lower surfaces of the contact elements in a given group from the contact plane lies within a narrow range.
U.S. patent application Ser. No. 10/802,993 filed Mar. 16, 2004 discloses an interconnect system that is able to accommodate the variations in distance between the confronting contact elements due to manufacturing tolerances when the contact plane of the connector is parallel to the contact plane of the corresponding group of contact elements of the DIB, but the interconnect system may not be able to accommodate the variations in distance between the contact elements of the connector and contact elements of the DIB in the event that the contact planes are significantly out of parallel.
One source of departures from parallelism of the contact plane of the connector and the contact plane of the corresponding contact elements of the DIB is nonuniformity in thickness of the DIB. Using conventional techniques it is possible to manufacture the DIB so that the upper and lower surfaces of the DIB are essentially planar, but it is more difficult to ensure that the upper and lower surfaces are parallel. For example, the DIB might vary in thickness by up to 2.5 mm along a diameter of the DIB. If the DIB is mounted so that its upper surface is horizontal, but the upper and lower surfaces of the DIB are not parallel, the lower surface of the DIB will not be horizontal.
When the lower surface of the DIB is generally horizontal, the contact plane of a connector might nevertheless not be parallel to the contact plane of the corresponding group of contact elements of the DIB because of local departures from horizontal of the lower surface of the DIB or because the connector is mounted in the support frame in a manner such that its contact plane is not horizontal.